Two Canadians, who were among thousands of foreigners stranded by anti-government protests in Bangkok, died when their van crashed on the way to catch a flight out of Thailand, police said on Tuesday.

Four other tourists, including three more Canadians, were injured in the crash, which happened as they made the 900-kilometre drive from Bangkok to the southern resort town of Phuket. Their identities haven't been disclosed.

They were making the trip because they could not fly out of Bangkok's besieged Suvarnabhumi airport, which has been shut by thousands of protesters seeking to oust Prime Minister Somchai Wongsawat.

Tens of thousands of frustrated tourists delayed for days by the protests, which have closed Suvarnabhumi and Bangkok's main domestic airport, have been seeking alternative ways out of Thailand.

The injured included three Canadians and a Briton, police Sub-Lieut. Chakrit Nina told Reuters.

"It is still to be determined whether the Thai driver dozed off during the long ride or, to take his word, he was attempting to avoid a pothole and a car," the officer said.

The driver passed an initial breathalyzer test but was detained for reckless driving causing death and injuries, Chakrit said.

The Bangkok-Phuket highway is one of the busiest routes in the country. It is mostly a divided freeway, but accidents and breakdowns occur frequently. It takes about 10 hours to do the journey by car, longer by van or bus.

Most of the stranded tourists are attempting to leave via the Vietnam War-era U-Tapao military airbase around 200 km from the capital, but others are trying via Phuket or Chiang Mai in the north.

Canadian Foreign Affairs Minister Lawrence Cannon said Monday that his government estimated "upwards of 1,000 Canadians" were affected by the airport shutdowns in Thailand.

With files from Reuters